Burgess Shale

Haplophrentis carinatus(Hyolithid - extinct group)

This interesting looking, shelled creature comprises three parts: A long, flat-bottomed, conical shell housing the body, a small lid (operculum) closing the front end, and two curved appendages sticking out sideways, like props, at the front. (Dr. Walcott named these side arms as "helens" after his daughter!) Presumably the helens acted as struts or stabilizers to keep the body from rolling around sideways in the currents. They may have also worked like oars, sculling the creature slowly along the bottom as it fed on organic stuff in the mud. In turn, these hyoliths served as food for other animals. Specimens have been found lined up, head-to-tail, in the gut of the sand-dweller, Ottoia.

These creatures were small - from about a 1/10th of an inch up to 1 1/4 inches in length. That, plus a slow method of locomotion must have made them ready "game" for the more active predators. (See the Burgess Shale site reconstruction.) Their unusual morphology makes it difficult to trace their affinities to other animals, although some scientists regard them as mollusks.